Our invention is directed to a prosthetic heart valve with an improved suture ring and to a method for securing the suture ring to the heart valve.
A standard implantable mechanical heart valve usually has an annular valve housing or body to provide a passageway for blood. Leaflets are mounted in the annular body and open or close the blood flow passageway. Usually there are one or two leaflets, but occasionally triple leaflet configurations have been proposed. On the outside of the valve body there is usually a circumferential groove. This groove is used to attach of a suture ring to the valve body.
The suture ring is used to sew the heart valve to the patient's heart tissue. The ring generally comprises a knit fabric tube which is rolled into a toroidal form and which is secured about the heart valve body in the circumferential groove. Various methods and apparatus have been proposed for securing the suture ring to the heart valve. It is known, for instance, to bind the ring into the groove with a plastic thread. It has also been proposed to form a rotatable suture rings on the heart valve using heat shrinkable plastic material, as disclosed in U.S. Pat. No. 3,781,969. U.S. Pat. No. 3,491,376 suggests that a suture ring should be formed as a separate sub-assembly which should then be attached to the heart valve. In the '376 patent, the suture ring is described as including a resilient annular member which is temporarily deformed, so as to snap the ring onto the valve body. U.S. Pat. No. 3,579,642 proposes the use of metal snap rings which must be radially expanded to place the suture ring about the valve body. In such fabrication techniques, however, there is a risk of potential damage to the suture rings when the ring is mechanically expanded to place it about the valve body.
In U.S. Pat. No. 4,743,253, Magladry proposed a two-part suture ring comprising the knit fabric and an internal crescent-shaped ring which would be deformed inwardly by electromagnetic forming to clamp the heart valve while permitting relative rotation between the suture ring and the heart valve.
In U.S. Pat. No. 5,071,431, two of us (Sauter and Campbell) and Poehlmann, disclosed a suture ring comprised of essentially three parts: a stiffening ring which fits over an outer surface of a heart valve; a knit fabric sewing cuff attached to the stiffening ring, and a locking band for securing the stiffening ring to the heart valve.
It has been found that the efficiency of a prosthetic heart valve is most dependent on the size of the valve. In other words, improved hemodynamic characteristics can be expected if the central orifice of the heart valve is made as large as possible with respect to the patient's anatomy. To accomplish this goal, the suture ring assembly, with its associated stiffening ring, should be made as thin radially as possible. In the past, suture ring-stiffening ring combinations have most frequently been made with three metallic components: a central stiffening ring and an upper and lower capture ring to capture the knit fabric tube of the sewing ring. To hold the upper and lower rings in position, the stiffening ring has frequently been formed with grooves to retain the capture rings against an outer side of heart valve annular body. This results in additional radial bulk. To overcome this problem, the assignee of our invention has heretofore attempted to employ spring loaded capture ring to allow the sewing ring to be placed over the stiffening ring after assembly, eliminating the grooves in the stiffening ring. This solution has not been completely satisfactory. There remains a need, therefore, for an improved sewing ring used in conjunction with a stiffening ring to minimize the overall radial thickness of the ring.